1. Field of the Invention
The present invention relates to an electronic control unit having a microprocessor built-in for use e.g., in a fuel supply control of an automobile engine and, more particularly, to an electronic control unit that comprises a plurality of control circuit sections electrically divided so as to carry out a mutual communication of serial signals, and includes improved error determination means for serial communication.
2. Description of the Related Art
Electronic control unit in which information exchange by a method of serial communication is carried out among a plurality of microprocessors sharing functions, and communication error is detected to carry out error processing, has been practically and widely used in various fields.
For example, according to the Japanese Patent Publication (unexamined) No. 219720/1997, the following method and unit for detecting failure in a communication network is proposed. In this method and unit, data that comes in via a communication network is obtained, whether or not a data error occurs is detected, and it is checked whether or not the number of data errors having been detected by the above-mentioned procedure exceeds a predetermined value within a predetermined time period. Further, it is arranged such that in the case of exceeding the above-mentioned predetermined value, a transmission error is determined to occur in the above-mentioned communication network; while in the case of being not more than the above-mentioned predetermined value, a transmission error is determined not to occur in the above-mentioned communication network; and a failure in the communication network will be detected based on this determination result of the transmission error. In this manner, it is possible to perform appropriate switching of a duplex system without being sensitively responsive also to a transitional error, thereby enabling to improve efficiency in maintenance.
In addition, according to the Japanese Patent Publication (unexamined) No. 162814/1997, the following communication-monitoring unit is proposed. This communication monitoring unit comprises a communication control section that controls data communication and outputs an error notification signal upon detecting any communication error, an error counter that counts up in response to the input of the above-mentioned error notification signal, and an annunciation section that announces a communication error in response to the fact that a count value of this error counter has reached a plus predetermined value (threshold). In this communication-monitoring unit, there is provided counter subtraction means that counts down a count value of the above-mentioned error counter upon the fact that the control of data communication is normally carried out in the above-mentioned communication control section. Further it is arranged so as to prevent an alarm generation in vain with respect to a sporadic and chronic error in which an error state automatically recovers, while immediately making an annunciation with respect to a fatal and continuous failure.
Further, according to the Japanese Patent Publication (unexamined) No. 267948/2000, the following electronic device or a control method thereof is proposed. This electronic device comprises a first unit having a first computer and a second unit that includes a second computer, and is constructed detachably with respect to the above-mentioned first unit. In this electronic device, the above-mentioned first computer comprises means for transmitting an operation confirmation signal in order to confirm the operation of the above-mentioned second computer to the above-mentioned second computer at intervals of a predetermined time period; and the above-mentioned second computer comprises means for replying an in-operation signal indicating a normal operation in response to the above-mentioned confirmation signal at the time of normal operation. Further, the above-mentioned first computer comprises means for resetting the above-mentioned second computer in the case where the above-mentioned in-operation signal is not replied within a predetermined standby time period to the transmission of the above-mentioned operation confirmation signal, and reliably resets the second computer when the second unit is mounted.
Furthermore, according to the Japanese Patent Publication (unexamined) No. 108835/2002, the following on-vehicle electronic control unit is proposed. This on-vehicle electronic control unit comprises serial communication means capable of transferring a control constant at the time of starting the operation, and mutually communicating without restraint a variety of data during the operation, and carries out a sum check error and a retransmission processing with respect to a serial communication data, a timeout check error and a reset processing of a microprocessor, or an inhibition processing of a control output.
As for the rest, in association with this invention, according to the Japanese Patent Publication (unexamined) No. 235598/2002, the following vehicle control unit is supposed. This vehicle control unit includes error occurrence storage means for restarting a microprocessor after having assured safety when the microprocessor such as main CPU or sub CPU, which is contained in any on-vehicle electronic device, runs away. However, the one that is described in this publication does not relate to a communication control.
In the method and unit for detecting failure in a communication network that is described in the above-mentioned Japanese Patent Publication (unexamined) No. 219720/1997, a count value of data errors is reset at intervals of a predetermined time period.
Accordingly, a problem exists in that number of times of acceptable error left for the error determination changes suddenly before and after the reset, resulting in lack of sequential continuity. In addition, any timeout error processing or any retransmission processing is not described from a comprehensive standpoint.
Furthermore, according to a communication-monitoring unit described in the above-mentioned Japanese Patent Publication (unexamined) No. 162814/1997, there are the following problems.
A problem exists in that a response delay is generated in detection of the error occurrence after a normal communication has continuously been carried out in case of setting a threshold value for determining the error to be large; and another problem in that a too-sensitive error detection is carried out also with respect to slightly sporadic error occurrence in case of setting a threshold value for determining the error to be small.
In addition, as for the Japanese Patent Publication (unexamined) No. 219720/1997, any timeout error processing or any retransmission processing is not mentioned from a comprehensive standpoint.
Besides, according to an electronic device or a control method thereof that is described in the above-mentioned Japanese Patent Publication (unexamined) No. 267948/2000, a problem exists in that a computer is reset only with a single timeout. In addition, a sum check error processing or a retransmission processing is not described from a comprehensive standpoint.
Further, according to an on-vehicle electronic control unit that is described in the above-mentioned Japanese Patent Publication (unexamined) No. 108835/2002, there are the following problems. A problem exists in that a microprocessor is reset with just a single timeout, or an output inhibition processing is carried out resolutely; another problem in that number of times of retransmission corresponding to any sum check error is not defined reasonably.
Moreover, according to a vehicle control unit that is described in the above-mentioned Japanese Patent Publication (unexamined) No.235598/2002, a problem exists in that although a timeout of communication attributed to the run-away error of a microprocessor can be detected, a timeout of the communication due to any other cause cannot be detected.